Extended Forecast Discussion NWS Weather Prediction Center College Park MD 200 PM EST Sun Nov 22 2020 Valid 12Z Wed Nov 25 2020 - 12Z Sun Nov 29 2020 ...Overview and Guidance Evaluation... Global model guidance this morning has finally come into decent agreement on favoring southern stream cyclogenesis over the central Plains midweek before the cyclone weakens and heads toward the Great Lakes. The GFS still indicates more northern stream development across the Canadian prairies than the rest of the guidance. Models then show good agreement on taking a cold front across the Plains into late this week as deep moisture from the Gulf of Mexico returns. This is when models begin to diverge in the way they handle the interaction of the Gulf moisture with the approaching cold front and subsequent cyclogenesis during the weekend. The GFS is the more progressive and aggressive model with this cyclone while the ECMWF is much slower and less aggressive. Their ensemble means are in between these two extremes. Meanwhile, the 00 UTC Canadian favors cold air intrusion with little in the way of cyclogenesis. The WPC medium range product suite was derived from a blend of the 00 UTC ECMWF/EC mean, the 06Z GFS/GEFS mean together with a smaller portion from the 00 UTC Canadian model to smooth less predictable smaller scale details. This yielded a solution in line with recent guidance trends and maintains good WPC continuity up to Day 5 Friday, with a faster eastward progression of the low pressure system across the South next weekend. ...Sensible Weather and Hazards... A separated southern stream shortwave trough/low aloft and well-organized surface low pressure/frontal system will produce a progressive and wide swath of moderate rainfall over the eastern third of the nation Wed, lingering into New England into Thu before exiting with approach of an amplified northern stream trough. Upstream, progressive but energetic flow aloft will deliver another round of unsettled weather through midweek over the Northwest to include rain and higher elevation snows with highest totals over the Cascades and a secondary maximum into northwestern Wyoming. Trough/closing low energies aloft in an emerging and separated southern stream are slated to dig down through the West later week along with potential for some mixed wintry precipitation for the central to southern Rockies. System ejection and downstream cyclo/frontogenesis along with increasingly deep return moisture from the Gulf of Mexico should then promote enhanced to locally heavy rainfall next Fri into the weekend a likely focus across the Deep South. Kong/Schichtel Additional 3-7 Day Hazards information can be found on the WPC medium range hazards chart at: https://www.wpc.ncep.noaa.gov/threats/threats.php WPC medium range 500mb heights, surface systems, weather grids, quantitative precipitation, winter weather outlook probabilities and heat indices are at: https://www.wpc.ncep.noaa.gov/medr/5dayfcst500_wbg.gif https://www.wpc.ncep.noaa.gov/medr/5dayfcst_wbg_conus.gif https://www.wpc.ncep.noaa.gov/5km_grids/5km_gridsbody.html https://www.wpc.ncep.noaa.gov/qpf/day4-7.shtml https://www.wpc.ncep.noaa.gov/wwd/pwpf_d47/pwpf_medr.php?day=4 https://www.wpc.ncep.noaa.gov/heat_index.shtml